As a method for achieving a higher density on an optical disc, there is a method for achieving a higher density in a line density direction by shortening the channel bit length, i.e., the mark length. Another method is a method of making the track pitch narrower. If the density is made higher in the line density direction, however, a problem of increased inter-symbol interference occurs. Furthermore, if the track pitch is made narrower, a leak of information from an adjacent track (adjacent track crosstalk) increases. Methods for reducing the adjacent track crosstalk (hereafter referred to simply as crosstalk as occasion demands) are proposed.
For example, it is described in PTL 1 that crosstalk is canceled by supplying reproduced signals of a track that is a reproduction target and tracks located on both sides thereof to an adaptive equalizer unit and controlling tap coefficients in the adaptive equalizer unit.